The present invention relates to a method for producing a highly dispersed catalyst for use in a variety of technical fields such as organic synthesis, hydrogenation, oxdation, reduction, a fuel cell, electrolysis and so forth.
For producing a catalyst in a conventional manner, there are two typical methods such as a direct reducing method and a colloidal method.
In the direct reducing method, a salt of an objective metal is dissolved in a solution and a carrier is immersed in this solution. Then, a reducing agent such as formalin and hydrazine is added to the solution to deposit a metallic cluster. In this method, it is impossible to obtain a carried catalyst having the clusters of the unifcrm size, for instance, less than 30 .ANG..
In the colloidal method, the uniform minute clusters can be obtained, but in a method using a reducing agent such as sodium hydrosulfite (Na.sub.2 S.sub.2 O.sub.4) and sodium bisulfite (NaHSO.sub.3), the sulfur in the reducing agent is mixed in the obtained catalyst, which brings about disadvantages in many catalytic reactions. In order to remove the mixed sulfur from the catalyst, particular equipment as well as time is required. Accordingly, the operational efficiency for producing the catalyst is bad. On the other hand, in a method adding polyvinyl alcohol as a protecting agent for the colloid before an alcoholic reduction, it is very difficult to remove a great deal of the added polyvinyl alcohol after the reduction. When the solution is heated in order to remove the polyvinyl alcohol, the clusters grow and the cluster size is enlarged.
In another conventional method, a charge-transfer polyvinyl acetate polymer film is impregnated with a metallic ion and then the metal is deposited. In this case, the size of the obtained clusters is large, such as several hundreds .ANG., and the properties of the catalyst are poor due to the velocity control of the mass transfer in the film.